Hydraulic cushions for dies of ram type presses



Dec. 29, 1964 F. M. WILLIAMSON 3,163,144

HYDRAULIC CUSHIONS FOR DIES OF RAM TYPE PRESSES Filed Oct. 17, 1962 I; w ,7 II

2 Sheets-Sheet 1 #4 //4 INVENTOR.

Dec. 29, 1964 F. M. WILLIAMSON HYDRAULIC CUSHIONS FOR DIES OF RAM TYPE PRESSES Filed Oct. 17, 1962 2 Sheets-Sheet 2 INVENTOR XZay/ Mflkmsoz #7 7a rut/4 United States Patent 3,163,144 HYDRAULHC QUSHEONS FGR BEES 0F RAM TYPE ERESEEES Floyd M. Wiiiiamsen, Detroit, Mich, assignor, by mesne assignments, to National Bani; of Detroit, Detroit,

Mich, a national banking association Filed Oct. 17, 1962, Ser. No. 231,131 9 Claims. (@l. ll3-45) This invention relates to hydraulic cushions for mechanical presses for controlling movement of the die pads during press operation and has particular reference to a new and improved hydraulic system for a hydraulic cushion.

The hydraulic system of the present invention provides a predetermined resistance to movement of the die pad during the operation on the work which occurs upon closing of the press ram and includes a booster for supplying high pressure fluid for returning the die pad to its extended position for stripping the work from the die and controls which make the system flexible and readily adaptable for a wide range of conditions. The system herein disclosed is an improvement upon somewhat similar systems disclosed in my prior parent application hereinafter referred to.

A principal object of the invention is to provide a new and improved hydraulic system for a hydraulic cushion for a crank type press.

Another object of the invention is to provide a hydraulic system for a hydraulic cushion which is adapted to provide a lower pressure resistance for the cushion on the closing stroke of the press than the pressure available for stripping the work from the die upon the opening of the press.

Other and further objects of the invention will be apparent from the following description and claims and may be understood by reference to the accompanying drawings, of which there are two sheets, which by way of illustration show preferred embodiments of the invention and what I now consider to be the best mode of applying the principles thereof. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

In the drawings:

FIG. 1 is a schematic sectional view illustrating a mechanical press and a hydraulic cushion for a movable die pad of the press and the control system for the hydraulic cushion;

FIG. 2 is an elevational view illustrating one form of actuating means for the controls;

FIGS. 3 and 4 show modified actuating means for the controls; and

FIG. 5 is a schematic view of a modified form of the invention.

In FIG. 1 of the drawing there is illustrated a portion of a crank type press which includes a reciprocating ram carrying an upper die 12 and a lower die 14 mounted on a fixed bolster 16. The die 14 is provided with a vertically reciprocable die pad 13 which is engaged by the Work during the working or closing stroke of the press. A piston 22 is reciprocable within a hydraulic cylinder 24- and one or more cylinders 24 each with a piston 22 therein provide a hydraulic cushion reacting on the die pad 18 to control its movement both during the working stroke of the press and upon or during opening of the press to strip the work from the die 14.

The hydraulic system includes a tank 39 containing hydraulic fluid under pressure and supplied with air under pressure through an air pressure line 32 to maintain the hydraulic fluid at a predetermined relatively low regulated pressure in the tank, say, for example, about 100 3,153,144 Patented Dec. 29, 1964 lbs. per square inch, or less or more depending upon the operation being carried out on the press and the pressure normally desired 0n the hydraulic fluid in the system. The hydraulic cushion cylinder 24 is provided with an inlet and exhaust port 34 to which a line 36 is connected, with the other end of the line 36 communicating with a bore 38 in the block of valve 40. Block of valve 40 is provided with a bore 42 containing a normally closed pressure relief valve 44 which is reciprocable therein and normally engages a valve seat 46 under the influence of a spring 48 which is confined between the valve member 44- and a washer 50, and an adjusting screw 52 engages the washer 50 so that the strength of the spring 48 may be adjusted to permit the valve 44 to open when a predetermined pressure is reached in the line 35. The pressure at which the valve 44 is set to open may vary widely from a very low pressure just above tank pressure to a pressure of several thousands per square inch or more, depending on the press operation being carried out.

A passage 54 in the block of valve 40 intersects the valve chamber 42. and is connected by means of hydraulic line 56 to the lower end of the supply tank 30. When the ram of the press descends, the movable die pad 18 which is engaged by the work is forced downwardly, thereby moving the piston 22 downwardly in the cylinder 24 to force the hydraulic fluid therein out through the line 36. The pressure relief valve 44 provides a predetermined resistance above tank pressure to such movement of the die pad and, as soon as the pressure in the hydraulic cylinder 24 exceeds the pressure for which the valve 44 is set, it will open thereby allowing the hydraulic fluid to flow through line 56 back to the supply tank 30. As soon as the ram completes its working stroke, the pressure relief valve 44 will close under the influence of spring 48. In some cases the regulated low pressure maintained on the hydraulic fluid in the tank 30 is adequate to provide the desired resistance to movement of the die pad 18 upon the closing of the press ram, and when this situation exists, normally closed valve 49 in the by-pass 51 may be manually opened to cut the pressure relief valve 44 out of the return flow connection from the cylinder 24 to tank 30. However, for best control of movement of the die pad 18, it is preferable to set the pressure relief valve 44- to provide the desired resistance and to keep valve 49 closed.

Means comprising a booster unit 60 are provided for generating hydraulic fluid pressure in the cylinder 24 to strip the work from the die 14 and effect return movement of the die pad to its extended position. The booster unit includes a hydraulic booster cylinder 62 having a piston 64- therein and a larger diameter air cylinder 66 having a piston 63 therein, with the pistons 64 and 68 interconnected by a stem 70. The booster cylinder 62 is supplied with hydraulic fiuid from the tank 30 through a line 72 leading from the lower end of the tank 30 to a passage 74 in a valve body 76. A passage 78 intersects the passage 74 and is normally closed by a ball check valve 8%) located in a chamber 82 at the intersection of passages 78 and 8d, the latter leading to a bore 36 in the valve body 7d. The lower end of the bore 86 communicates with the discharge end of booster cylinder 62 above the piston 64 therein. The booster cylinder is filled with the hydraulic fluid from the tank 30 through the passages described. The upper end of the bore 86 is normally closed by a piston valve ht; which is reciprocable in sleeve 99 located in a recess in the valve body 76 and surrounded by an annular chamber 92 intersected by a passage 94 which leads to a line 96. Piston valve member 98 is biased by a spring liltl against a seat or shoulder 162. The valve sleeve 9b is provided with a series of annularly spaced radial ports lild which provide communication between the bore 86 and the line d6 when the valve ports 104 are open, and with a series of annularly spaced radial ports 195 which normally provide communication between the inside of sleeve 9% and line as above valve 92 The passage 74 communicates with the interior of sleeve 9% at the upper end thereof so that both sides of the valve member 98 are subjected to the pressure existing in the supply tank 3i Sleeve Bil, ports 104 and M5, piston 98 and spring 16% comprise a sleeve or piston type valve indicated generally at 88, elements 98, 104 of which function as a normally closed or check valve in the one-way hydraulic fluid connection between the booster cylinder 62 and cushion cylinder 24 and, together with check valve lltl, prevents return flow from cylinder 24 to cylinder 62. Elements 8, 1% of valve 38 form a normally open valve in the hydraulic fluid connection between tank 3% and cylinder 24 through which tank pressure is transmittted to cylinder 24 to bias piston 22 and pad 18 to their extended positions. Valve 88 separates the booster cylinder 62 from part of the hydraulic fluid connection 72, 74, 92, $6, 36 between tank 33 and cylinder 24 which makes it possible to operate the system without the booster 60 when the pressure generated thereby is not required for stripping purposes.

The line 96 is connected to a passage 1% in the block of valve 40 which communicates with a passage ltld leading to the bore 38 and the line 36, whereby hydraulic fluid is supplied under tank pressure to the cylinder 24. The passage N6 is provided with a check valve lit? to preclude return flow of hydraulic fluid from bore 38 into line )6.

The lower end of the air cylinder 65 below piston 68 is provided wi-th'a port 112 leading to a control or pilot rotary valve 114 which includes an air supply line port 116, an exhaust line pont 118, and a control lever 120' by means of which the cylinder port M2- may be connected either to the exhaust port 118 or the supply port 116 which is connected to a source of air under pressure, such as the upper end of pressure tank 30 or the air pressure supply line 32 therefor. The control lever 120 is actuated by a solenoid T122 and is urged by a spring 124 to a position in which the cylinder port 13.2 is connected to the exhaust line 118'. When the solenoid 122 is energized, the cylinder port 112 will be connected to the air pressure line 16.

The control. or pilot valve 114- is actuated by the solenoid 122 to effect actuation of the piston 68 at a predetermined time when or after the ram of the press begins its upward movement, depending on the Work being done on the press and the setting of the controls for the valve 114. The electrical circuit into which the solenoid 122 is connected may include a fixed contact 159 and a normally open movable contact 132 carried by a pivoted arm 1134 which is adapted to be engaged by a cam 136 carried by a. shaft $.38 which rotates with the crank of the press. The cam 36 is adjusted on the shaft 133 so as to close the contacts 134 and 132 at a selected time when or after the press ram begins to open during each cycle of the press. When the contacts close, the solenoid 122 is energized to shift the control valve 114 to connect the cylinder port 112 with the. supply line 116, thereby to actuate the boosterthat' is, force the piston 68 upwardly within the cylinder d6 thereby forcing the piston 64 upwardly to discharge the hydraulic fluid from cylinder 62; and force such fluid through the bore 86 to shift the valve member 98 upwardly to open the radial ports 1%. As soon as valve member 98 moves sufficiently to expose ports 1% and close ports N5, hydraulic fluid under booster pressure flows or reacts through line 96 and passages res and 183 and line 36 to increase the pressure in the hydraulic cushion cylinder 24 to react on the piston 22 therein and return it to its extended position if not previously so positioned by the tank pressure. The relative size of the pistons 68 and 64 greatly increases the pressure in the hydraulic cushion cylinder 24 above the regulated pressure at which the hydraulic fluid is normally maintained within the supply tank 30, thereby insuring return of the die pad 18 by piston 22 and stripping of the work from the die if tank pressure is insufficient for this purpose. The time when and the interval during which the booster 60 is energized is determined by the position and length of the earn. 136. As soon as the contacts 13% and 132 are opened, the solenoid is de-energized and the control lever 123 is then shifted by the spring 12 to connect the cylinder port 112 with the exhaust line 118 thereby allowing the booster pistons 64- and 68 to return to their lower position as the cylinder 62 is again filled with hydraulic fluid from the tank 30 in the manner described. The valve member 98 will also close as the piston 64 retracts since it is subjected to equal hydraulic pressures on its opposite sides and is urged to its closed position by the spring 1%. Cam 136 may be set to energize the booster as soon as the press ram begins to open or at some interval thereafter to effect a delay if desired in the return of the pad to its extended position it tank pressure is insufficient to strip the work from the die.

The connection between the supply tank 36 and line 96 is normally open through ports ltiS of the valve 88 and, since valve 9% is pressure balanced, the spring llliii may e very light to maintain valve 98, N5 in its normally open position as shown when the booster 6% is deenergized.

lnstead of using the solenoid actuated pilot valve 114, a spool type normally closed pilot valve 201 as shown in FIG. 3, actuated directly by the cam 136 may be used for controlling the operation of booster so and thereby the return of the die pad 1% as previously described. in this case the valve Elli, when closed, ports the line 112 communicating with cylinder 66 with line 113 leading to atmosphere, While the movable valve element 2&3 is normally positioned by the spring 2G4 so as to shut off the flow of air under pressure from the air supply line 116 to the passage 112-. When the cam 136 engages the roller on the follower arrn Zllli carried by the sliding valve member 293, the valve member 263 will be shifted to a position to shut oi the atmospheric port and to establish communication between the air pressure line 116 and the line 112 leading to the cylinder 66. The spring 294 causes the roller on the arm 2% to follow the cam 136. This type of valve control is like that shown in my prior copending application Serial No. 768,889, filed October 22, 1958, for Hydraulic Press Ram Cushion.

FIG. 4 shows a normally closed rotary pilot valve lid as shown in FIG. 1 arranged so as to be actuated directly by cam 136 so as to control the operation of thebooster 6t and the return of the die pad as previously described.

in the arrangement of FIG. 1, the pressure which can be developed on the cushion side of the valves 4% and 8%; upon the energization of the booster unit (all is limited by the pressure setting of the pressure relief valve to. In some cases it is necessary or desirable to provide a higher pressure in the hydraulic cushion on the upstroke for stripping purposes than on the downstroke, and this may be achieved with the system illustrated in FIG. 5 where the pressure relief valve is p essureisolated from the discharge side of the booster unit let).

in the system as disclosed in FIG. 5 hydraulic fluid under the pressure prevailing in the tank 3%! is supplied through the hydraulic fluid pressure line 172 to the valve unit indicated generally at 171. Hydraulic fluid under tank pressure is also supplied through line 173 and a oneway by-pass around the pressure relief valve dill, as in FIG. 1, and through line 1'75 and valve 1'71 and line 177 to the cylinder 24-. The valve unit 1'71 is quite similar to the corresponding valve 83 of the system in FIG. 1 and includes a passage 178 communicating with the line 172, a check valve 18% in the passage 1'78, and a passage 186 which at one end communicates with the discharge end of hydraulic cylinder 162 of the booster 160. The other end of the passage res communicates with a valve chamber in the unit 171, the valve chamber having disposed therein a valve sleeve 188 and a valve piston 190 biased to seat on the port around the upper end of passage 186 under the influence of spring 192. Thus under the pressure prevailing in the tank 30, hydraulic fluid is supplied through the line 172 past the check valve 180 to the passage 186 and to the booster cylinder 162 for charging the latter when the booster is de-energized as in FIG. 1.

When the piston valve member 190 is moved upwardly in response to the discharge of hydraulic fluid from the booster cylinder 162, it uncovers ports 200 in the sleeve 188 which communicate with the space externally of the sleeve 188, which in turn communicates with a passage 202 in the unit 171 and closes ports 206. At its upper end the passage 202 communicates with hydraulic fluid pressure conduit 1'77 which leads to the hydraulic cylinder 24 of the hydraulic cushion. Thus, when the valve ports 200 are uncovered and the valve ports 206 closed, hydraulic fluid pressure generated by actuation of the booster 160 will be supplied to the cylinder 24 of the hydraulic cushion for biasing the piston 22 against the pad 18 and returning the pad to its extended position if the tank pressure was insuflicient for such purpose. As the piston valve 190 moves upwardly in the sleeve 188, it closes valve ports 206 in the sleeve 188 which normally provide open communication between the passage 1'77 and hydraulic pressure line 175 which communicates through the by-pass around the pressure relief valve 40 with tank 30.

Thus the energization of the booster according to any of the arrangements disclosed in FIGS. 1-5 inclusive will raise the pressure in hydraulic cylinder 24 above tank pressure and insure stripping of the work from the die. With the arrangement illustrated in FIG. 5, the booster can develop substantially higher pressures in the cylinder 24 on the upstroke of the press ram than is developed or available on the downstroke during closing of the press ram since the pressure relief valve 40 is pressure isolated from the discharge side of the booster. This make it possible to use very high .presnres for stripping. After the de-energization of the booster 160, tank pressure will return the piston valve 198 to its seat as shown in FIG. 5 and open valve ports 2% so as to leave the cylinder 24 under tank pressure. The system as illustrated in FIG. 5, using any of the controls as disclosed in FIGS. l4, in other respects will operate as described in connection with the systems illustrated in FIGS. 14.

If pressure in excess of tank pressure is not required or desired for stripping purposes, the controls for actuating the booster can be temporarily disconnected and the system operated without the booster. When the booster is hooked up for normal operation during cycling of the press, by manually closing the normally open valve 210 in the by-pass 1%, 108 on the cushion side of check valve 110, cylinder 24 will be cut oft from tank pressure and can be recharged only by actuation of the booster and in such event the booster can be actuated as previously described after the press ram begins to open so as to delay return of the piston 22 to its extended position and thereby stripping of the work from the die. For best performance in use, pressure relief valve 48 preferably should be constructed in accordance with the disclosure of my prior Patents 2,901,238 and 2,938,718.

This application is a continuation-in-part of my prior copending application Serial No. 190,542, filed April 27, P

1962, to replace Serial No. 84,900, filed January 25, 1961, for Hydraulic Cushions for Die Pads of Ram Type Presses, which is a continnation-in-part of my prior copending application Serial No. 832,720, now Patent No. 3,089,375, filed August 10, 1959, for Hydraulically Actuated Piercing Unit, which is a coin donation-impart of my now abandoned application Serial No. 788,544, filed January 23, 1959, for Hydraulically Actuated Piercing Unit. This application is also a continuation-in-part of my applications Serial No. 35,648, now Patent No. 3,059,914, filed June 13, 1960, and Serial No. 768,889, new Patent No. 3,085,530

led October 22, 1958, as a continuation-in-part of my September 10, 1954, application which matured into Patent No. 2,890,669 on June 16, 1959.

While I have illustrated and described preferred embodirnents of my invention, it is understood that these are capable of modification, and I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a mechanical press having a movable pressure pad engaged by the work so as to be retracted upon closing of the press ram, a hydraulic cushion including a cylinder and piston disposed to react against said pad to resist such movement and to effect return movement or" the pad to its extended position upon opening of the press, a pressure tank separate from said cylinder and containing hydraulic fluid under relatively low pressure, a booster cylinder and piston separate from said tank, unidirectional flow hydraulic fluid connections between said tank and booster cylinder and one end of said hydraulic cushion cylinder through which hydraulic fluid is free to flow under tank pressure from said tank to said cylinders when said booster is inactive whereby tank pressure is transmitted to said piston for biasing it and said pad toward their extended position and said booster cylinder is charged with hydraulic fluid under tank pressure, a hydraulic fluid flow connection between said booster cylinder and said one end of said hydraulic cushion cylinder, 2. control valve for connecting said booster to a source of pressure fluid which upon opening of said valve actuates said booster piston in a direction to discharge hydraulic fluid from said booster cylinder to substantially increase the pressure of the hydraulic fluid in said hydraulic cushion cylinder to effect return movement of said. piston and pad to their extended position, control means for said valve actuated by the press for opening said valve to effect actuation of said booster piston at a predetermined time during the opening portion of each cycle of the press, said booster being inactive during the cycling of the press except when actuated under the control of said control valve and control means, a normally open valve in the hydraulic connection through which hydraulic fluid is free to flow from said tank to said cushion cylinder when said booster is inactive, said normally open valve being arranged to be closed by hydraulic fluid discharged by and upon actuation of said booster piston, a fluid return line from said one end of said hydraulic cushion cylinder to said tank through which hydraulic fluid displaced from said hydraulic cushion cylinder is returned to said tank due to retraction of said die pad upon closing of the press ram, and a normally closed pressure relief valve in said return line providing a predetermined resistance higher than tank pressure to return flow of such displaced fluid and retraction of said die pad and adapted to open when the pressure in said hydraulic cushion cylinder exceeds a predetermined pressure.

2. In a mechanical press having a movable pressure pad engaged by the work so as to be retracted upon closing of the press ram, a hydraulic cushion including a cylinder and piston disposed to react against said pad to resist such movement and to effect return movement of the pad to its extended position upon opening of the press, a pressure tank separate from said cylinder and containing hydraulic fluid under relatively low pressure, a booster cylinder and piston separate from said tank, unidirectional flow hydraulic connections between said tank and booster cylinder and one end of said hydraulic cushion ,2 cylinder through which hydraulic fluid is free to flow under tank pressure from said tank to said cylinders when said booster is inactive whereby tank pressure is transmitted to said piston for biasing it and said pad toward their extended position and said booster cylinder is charged with hydraulic fluid under tank pressure, a hydraulic fluid flow connection between said booster cylinder and said one end of said hydraulic cushion cylinder, means for controlling theactuation of said booster whereby said booster piston discharges hydraulic fluid from said booster cylinder and thereby increases the pressure of the hydraulic fluid in said hydraulic cushion cylinder to effect return movement of said pad at a predetermined time during the opening portion of each cycle of the press, said booster being inactive during the cycling of the press except when actuated under the control of said control means, a normally open valve in the hydraulic connection between said tank and cushion cylinder through which hydraulic fluid is free to flow from said tank to said cylinder when said booster is inactive, said normally open valve being subject to and closed by hydraulic fluid discharged by and upon actuation of said booster piston, a fluid return line from said one end of said hydraulic cushion cylinder to said tank through which hydraulic fluid displaced from said hydraulic cushion cylinder is returned to sand tank due to retraction of said die pad upon closing of the press ram, and a normally closed pressure reliei valve in said return line providing a predetermined resistance substantially higher than tank pressure to return flow of such displaced fluid and retraction of said die pad and adapted to open when the pressure in said hydraulic cushion cylinder exceeds a predetermined pressure.

3. Apparatus according to claim 2 wherein said return line and said hydraulic flow connection between said cylinders are interconnected so that said pressure relief valve is subjected to the discharge pressure of hydraulic fluid discharged by said booster when the latter is actuated.

4. Apparatus according to claim 2 wherein portions of said return line and said hydraulic flow connection between said cylinders are separated so that said pressure relief valve is pressure isolated from the dischar e pressure of hydraulic fluid discharged by said booster.

5. Apparatus according to claim 2 wherein said normally open valve comprises a sleeve having two sets of ports, one set of, such ports being in the hydraulic flow connection between said cylinders and the other set of ports being in the hydraulic fluid connection between said tank and hydraulic cushion cylinder and a piston valve member biased to normally close said one set of ports.

6. Apparatus according to claim 5 wherein said hydraulic flow connection between said tank and hydraulic cushion cylinder and said return line are independent of said booster cylinder whereby said apparatus will function as a hydraulic cushion during cycling of the press without requiring operation of said booster.

7. In a mechanical press having a movable pressure pad engaged by the work so as to be retracted upon closing of the press ram, a hydraulic cushion including a cylinder'and piston'disposed to react against said pad to resist such movement and to eltect return movement of the pad to its extended position upon opening of the press, a pressure tank separate from said cylinder and containing hydraulic fluid under relatively low pressure, a booster cylinder and piston separate from said tank, hydraulic fluid flow connections between said tank and booster cylinder and one end of said hydraulic cushion cylinder through which hydraulic fluid is free to flow under tank pressure'from said tank to said cylinders to charge said cylinders with hydraulic fluid under tank pressure when said booster is inactive, a one-way fluid flow connection through which hydraulic fluid flows from said booster cylinder to said one end of said hydraulic cushion cyling o'er, said booster being inactive except when said piston is operable to discharge hydraulic fluid from said booster c r crease the pressure of the hydraulic fluid in der to u said hydraulic cusrion cylinder to effect return movement of said pad at a predetermined time during the opening portion of each cycle of the press, a normally o valve in the hydraulic connection between said tank and cushion cylinder, said normally open valve being exposed to and closed by hydraulic fluid discharged by and operation of booster piston, a fluid return line from said one end of said hydraulic cushion cylinder to said tank through which hydraulic fluid displaced from said hydraulic cushion cylinder returns to said tank due to retraction of said die pad upon closing of the press rain, and a normally closed pressure relief valve in said return line providing a predetermined resistance substantially higher than tank pressure to return flow of such displaced fluid and to retraction of said die pad and adapted to open when the press-are in said hydraulic cushion cylinder exceeds a predetermined pressure, said normally open valve including a alve member separating said return line and said fluid flow connections between said cylinders so that said pressure relief valve is pressure isolated from discharge pressure of hydraulic fluid discharged from said booster cylinder when the booster is actuated.

S. In a press having a movable pressure pad engaged by the work so as to be moved in one di ection during closing of the press rant. a hydraulic cushion including a cylinder and piston reacting against said pad to resist such movement and to effect return movement of the pad, a pressure tank separate said cylinder and containing hydraulic fluid ur ier regizlated pressure, a booster cylinder and piston separate from said tank, hydraulic fluid flow connections between said tank and one end of each of said cylinders and between ends of said cylinders arranged so that hydraulic fluid is free to flow under tank pressur from said tank to said cylinders to charge said nders with hydraulic fluid under tank pressure when s'ud booster is inactive, means to actuate said booster piston to disci ge hydraulic fluid from said booster cylinder to increa, the pressure of hydraulic fluid in said hydraulic cushion cylinder to effect return movement of said pad at a predetermined time during the opening portion of each cy le of the press, a normally open valve in the hydraulic flow connection between said tank and hydraulic cushion cylinder arranged to be closed by hydraulic fluid discharged by and upon actuation of said booster piston, said hydraulic flow connection including provisions for returning hydraulic fluid displaced from said one end of said hydraulic cushion cylinder to said tank. due to movement or" said pad in said one direction upon closing of the press ram, against a. pressure resistance at least as high as tank pressure to provide a predetermined re sistance to movement oi said die pad in said one direction.

9. Apparatus according to claim 8 wherein said valve is arranged in said connections so that the dis harge pressure of the hydraulic fluid discharged from said booster cylinder is higher than the pressure resistance to discharge of hydraulic o from said cushion cylinder during closing of the press ram.

References Qited by the Examiner UNITED STATES PATENTS 1,745,549 Z/SG lvlarghitan l1346 1,777,130 9/30 Rode 113-46 2,172,853 9X39 Rode 267-1 2,3G5,610 1 Ernst ll346 2,584,339 2/52 Georgefl 113-46 CHARLES W. LANl-lAh'i, Primary Examiner. 

1. IN A MECHANICAL PRESS HAVING A MOVABLE PRESSURE PAD ENGAGED BY THE WORK SO AS TO BE RETRACTED UPON CLOSING OF THE PRESS RAM, A HYDRAULIC CUSHION INCLUDING A CYLINDER AND PISTON DISPOSED TO REACT AGAINST SAID PAD TO RESIST SUCH MOVEMENT AND TO EFFECT RETURN MOVEMENT O F THE PAD TO ITS EXTENDED POSITION UPON OPENING OF THE PRESS, A PRESSURE TANK SEPARATE FROM SAID CYLINDER AND CONTAINING HYDRAULIC FLUID UNDER RELATIVELY LOW PRESSURE, A BOOSTER CYLINDER AND PISTON SEPARATE FROM SAID TANK, UNIDIRECTONAL FLOW HYDRAULIC FLUID CONNECTIONS BETWEEN SAID TANK AND BOOSTER CYLINDER AND ONE END OF SAID HYDRAULIC CUSHION CYLINDER THROUGH WHICH HYDRAULIC FLUID IS FREE TO FLOW UNDER TANK PRESSURE FROM SAID TANK TO SAID CYLINDERS WHEN SAID BOOSTER IS INACTIVE WHEREBY TANK PRESSURE IS TRANSMITTED TO SAID PISTON FOR BIASING IT AND SAID PAD TOWARD THEIR EXTENDED POSITION AND SAID BOOSTER CYLINDER IS CHARGED WITH HYDRAULIC FLUID UNDER TANK PRESSURE, A HYDRAULIC FLUID FLOW CONNECTION BETWEEN SAID BOOSTER CYLINDER AND SAID ONE END OF SAID HYDRAULIC CUSHION CYLINDER, A CONTROL VALVE FOR CONNECTING SAID BOOSTER TO A SOURCE OF PRESSURE FLUID WHICH UPON OPENING OF SAID VALVE ACTUATES SAID BOOSTER PISTON IN A DIRECTION TO DISCHARGE HYDRAULIC FLUID FROM SAID BOOSTER CYLINDER TO SUBSTANTIALLY INCREASE THE PRESSURE OF THE HYDRAULIC FLUID IN SAID HYDRAULIC CUSHION CYLINDER TO EFFECT RETURN MOVEMENT OF SAID PISTON AND PAD TO THEIR EXTENDED POSITION, CONTROL MEANS FOR SAID VALVE ACTUATED BY THE PRESS FOR OPENING SAID VALVE TO EFFECT ACTUATION OF SAID BOOSTER PISTON AT A PREDETERMINED TIME DURING THE OPENING PORTION OF EACH CYCLE OF THE PRESS, SAID BOOSTER BEING INACTIVE DURING THE CYCLING OF THE PRESS EXCEPT WHEN ACTUATED UNDER THE CONTROL OF SAID CONTROL VALVE AND CONTROL MEANS, A NORMALLY OPEN VALVE IN THE HYDRAULIC CONNECTION THROUGH WHICH HYDRAULIC FLUID IS FREE TO FLOW FROM SAID TANK TO SAID CUSHION CYLINDER WHEN SAID BOOSTER IS INACTIVE, SAID NORMALLY OPEN VALVE BEING ARRANGED TO BE CLOSED BY HYDRAULIC FLUID DISCHARGED BY AND UPON ACTUATION OF SAID BOOSTER PISTON, A FLUID RETURN LINE FROM SAID ONE END OF SAID HYDRAULIC CUSHION CYLINDER TO SAID TANK THROUGH WHICH HYDRAULIC FLUID DISPLACED FROM SAID HYDRAULIC CUSHION CYLINDER IS RETURNED TO SAID TANK DUE TO RETRACTION OF SAID DIE PAD UPON CLOSING OF THE PRESS RAM, AND A NORMALLY CLOSED PRESSURE RELIEF VALVE IN SAID RETURN LINE PROVIDING A PREDETERMINED RESISTANCE HIGHER THAN TANK PRESSURE TO RETURN FLOW OF SUCH DISPLACED FLUID AND RETRACTION OF SAID DIE PAD AND ADAPTED TO OPEN WHEN THE PRESSURE IN SAID HYDRAULIC CUSHION CYLINDER EXCEEDS A PREDETERMINED PRESSURE. 